Although they are harmful, most organisms do not specifically eliminate transposons from their DNA. Such a massive intervention might bear too much of a risk for germ cell genomes and hence a species reproductive fitness. To deal with the potential dangers, plants and animals possess defense systems – also seen as sort of a ‘genome immune system’.
In all cases, these are based on small RNA silencing mechanisms and hence date probably back to the early days of eukaryotic evolution. The ancient silencing systems are able to selectively interfere with transposon expression preventing them from causing damage.
In animals, the most prominent of these silencing pathways is the so-called piRNA pathway. At its core act so-called RNA induced silencing complexes (RISC) that are composed of PIWI proteins bound to 22-30nt long piRNAs. Via the small RNA, PIWI complexes recognize transposon RNAs and this induces degradation of the transposon RNA and feeds back negatively on the encoding locus on the host DNA to inhibit transposon transcription.
With their recent work, Brennecke and his team made a major step forward in the dissection of the piRNA pathway. With a mix of genetic, molecular and computational methods the team performed a screen in the Drosophila ovary for factors involved in the piRNA pathway. All in all they examined 7,000 different genes and manually inspected around 60.000 fruitflies for defects in transposon silencing.Fly library as goldmine of knowledge
In their two years of work, Brennecke and his group discovered around 50 genes that are important for a fully functional piRNA pathway. Dominik Handler, PhD student in Brennecke’s lab and first author of the study, explains: “For many of the identified genes, orthologous genes can be identified in the human genome, too. Our results will therefore have a broad impact on the general understanding of this transposon silencing system.” Some of the identified genes are required for the biogenesis of piRNAs, but others connect the defense system to basic processes such as mitochondria-metabolism, RNA transport, transcription or chromatin-biology.Signalling-pathway with great potential
Original publication: The Genetic Makeup of the Drosophila piRNA Pathway, Molecular Cell, Doi: 10.1016/j.molcel.2013.04.031Julius Brennecke:
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